The demand for increased capacity of magnetic recording media has resulted in the development of magnetic thin film recording media, such as disk-shaped magnetic thin film recording media (hereinafter simply referred to as magnetic thin film disks), by suitable scaling of both growth and magnetic properties of the magnetic thin film recording layer (hereinafter simply referred to as the magnetic thin film). The magnetic thin film disk should have a high and controllable coercivity, preferably in the range of 2000 Oe to 5000 Oe, and a high remanent magnetization greater than 0.8. Co-based alloys such as CoPtCr, CoCrPtB and CoCrPtTaB are commonly used for the magnetic thin film. The magnetic thin film is deposited on a nonmagnetic substrate, such as NiP-coated Al, AlMg and glass substrates. In order to overcome the problems of high striction and friction, the surface of the substrate is roughened prior to the deposition of the magnetic thin film, by one of the common mechanical abrasive techniques known as texturing. Mechanical texturing made of the coated substrate have shown to improve the media signal-to-noise ratio (SNR).
The orientation of the axis of easy magnetization (hereinafter simply referred to as the easy axis) of Co in the Co-based magnetic thin film is an important artifact due to the texturing and proper selection of the underlayer disposed under the magnetic thin film. The mechanical texturing eventually gives rise to an orientation ratio of the magnetic thin film, calculated by the ratio of coercivities along the radial direction to that of the circumferential direction in the case of the magnetic thin film disk. However, the origin or orientation ratio was conventionally not clear and was not established clearly. The underlayer structure used normally for good in-plane orientation of the easy axis of the Co in the Co-based magnetic thin film is based on a Cr underlayer deposited at different conditions. In order to improve the media SNR for ultra high-density recording, there is a necessity to grow the crystallographic c-axis of Co in the Co-based magnetic thin film preferentially along the circumferential direction in the case of the magnetic thin film disk.
The Cr(002) texture of the Cr underlayer is essential to grow the Co-based magnetic thin film to have a preferential growth of the Co(1120). This is usually achieved because the lattice matching of Cr(002) and Co(1120) is very good, that is, the mismatch is only 0.5% and 5% respectively along the length and breadth of the lattice. Moreover, the Co(1120) growth allows the magnetization to lie in-plane which is essential for the longitudinal magnetic recording. When the Cr underlayer is grown with the Cr(002) texture, the Cr(002) plane of the individual grains in the Cr underlayer is random within the plane. In other words, the Cr<110> is random within the plane. This is true when there is no mechanical texturing of the substrate and believed to be the same even after the mechanical texturing. Hence, the origin of the orientation ratio of the magnetic thin film was not so clear.
For better crystallographic c-axis orientation and good orientation ratio, the Cr<110> preferred growth along the circumferential direction is a necessary requirement in the case of the magnetic thin film disk. If any other orientation such as the Cr<002> exists along the circumferential direction, an epitaxial growth with the Co crystallographic c-axis preference along the circumferential direction, that is, the mechanically textured direction, is not possible.